User equipment in a congestion controlled CDMA system

ABSTRACT

A user equipment (UE) configured for use in a wireless code division multiple access (CDMA) system with multi-user detection capabilities that implements congestion control includes a receiver having multi-user detection capabilities, an intra-cell interference measuring device, and an intra-cell interference signaling device. The intra-cell interference signaling device is configured to transmit signals indicative of intra-cell interference from which congestion control is based.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/265,046, filed on Oct. 4, 2002, which claims priority from U.S.Provisional Application No. 60/383,025, filed on May 24, 2002, which areincorporated by reference as if fully set forth.

BACKGROUND

The present invention relates to code division multiple access (CDMA)systems with multi-user detection (MUD) capabilities, where the capacityof the system is limited by non-cancelled intra-cell interference,non-cancelled inter-cell interference and interference associated withthe noise floor.

In CDMA systems, one of the factors that limits the capacity of thesystem is interference. In general, these systems try to generate aslittle interference as possible. Power control is one approach that iscommonly used in order to maintain the interference limits as low aspossible. Nevertheless, when a CDMA system attempts to support manyusers, even if the transmission power is being controlled, the levels ofinterference may not be acceptable.

The concept of CDMA uplink (UL) pole capacity has been widely used forevaluating when a system is becoming congested. This concept is based onthe exponential growth of interference caused by a CDMA system, i.e. allinterference above the noise floor. The interference caused by a CDMAsystem is made up of intra-cell interference and inter-cellinterference. Intra-cell interference is interference generated in acell that is occupied by a user. Inter-cell interference, in contrast,is interference generated from all sources outside of the cell in whichthe user is located. The pole capacity is the theoretical maximumcapacity assuming the mobiles have infinite available transmittingpower. The actual capacity is typically a fraction of the pole capacity.Although the concept generally applies to any point-to-multipoint CDMAsystem, the use of a MUD in the receiver that cancels some of theintra-cell interference varies the principle on which the concept isbased thereby rendering the concept not applicable.

A method is therefore needed for evaluating congestion in CDMA systemshaving MUD capabilities.

SUMMARY

A user equipment (UE) configured for use in a wireless code divisionmultiple access (CDMA) system with multi-user detection capabilitiesthat implements congestion control is disclosed. The UE includes areceiver having multi-user detection capabilities, an intra-cellinterference measuring device, and an intra-cell interference signalingdevice. The intra-cell interference signaling device is configured totransmit signals indicative of intra-cell interference from whichcongestion control is based.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing a method for monitoring congestion inthe UL based on UE measurements for CDMA systems having MUD capabilitiesin accordance with an embodiment of the invention.

FIG. 2 is a flow diagram showing a method for monitoring congestion inthe UL based on RAN measurements for CDMA systems having MUDcapabilities in accordance with an embodiment of the invention.

FIG. 3 is a flow diagram showing a method for relieving congestion inaccordance with an embodiment of the invention.

FIG. 4 is a system for monitoring and controlling congestion in the ULbased on UE measurements in accordance with an embodiment of theinvention.

FIG. 5 is a system for monitoring and controlling congestion in the ULbased on RAN measurements in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

For uplink (UL) congestion detection based on UE measurements, the polecapacity of regular CDMA systems, i.e. CDMA systems not having MUDcapabilities, can be determined by measuring the noise rise, which isthe ratio of the total perceived interference to noise floor:

$\begin{matrix}{{Noise\_ rise} = {\frac{{total\_ perceived}{\_ interference}}{noise\_ floor} = \frac{1}{1 - \eta_{UL}}}} & {{Equation}\mspace{20mu}(1)}\end{matrix}$where the total perceived interference is all non-cancelled interference(both intra-cell and inter-cell) at the receiver, the noise floor is allnoise that is unrelated to the system such as the thermal noise, andη_(UL) is the UL load factor. In CDMA systems having MUD capabilities,however, the MUD reduces intra-cell interference (I_(or)) and amplifiesinter-cell interference (I_(oc)). Therefore, to accurately measure noiserise in CDMA systems having MUD capabilities, the η_(UL) should accountfor the affect the MUD has on interference.

To specifically account for the affect of the MUD, two parameters (oneto account for the decrease in I_(or) and one to account for theincrease in I_(oc)) are defined and incorporated into η_(UL). The firstparameter, α _(UL), represents the average ratio of the cancelled I_(or)to the total I_(or) and is used to account for the decrease in I_(or).The second parameter, β _(UL), represents the average ratio of receivedextra I_(oc) to the total I_(oc) and is used to account for the increasein I_(oc). The parameters α _(UL) and β _(UL) may be measured,calculated or assumed, as desired. Using I_(or), I_(oc), α _(UL) and β_(UL), the total perceived interference as affected by the MUD is (1− α_(UL))Ior+(1+ β _(UL))Ioc.

In a first embodiment of the invention, congestion detection is based onUE measurements. UE measurements, however, with respect to interferencegenerated by the system, are limited to I_(or). Therefore, to alsoaccount for I_(oc), η_(UL) is obtained according to:

$\begin{matrix}{\eta_{UL} = {\left( {1 + i} \right){\sum\limits_{j = 1}^{N}\frac{1}{1 + \frac{W}{\rho_{i}R_{i}v_{i}}}}}} & {{Equation}\mspace{14mu}(2)}\end{matrix}$where i is a predetermined value representing a ratio of I_(oc) toI_(or) and the sum represents I_(or). In the sum, N is the number ofusers in the cell; W is the carrier bandwidth; and ρ_(j), R_(j) andν_(j) are the signal-to-noise ratio (E_(b)/N₀) bit rate, and activityfactor of the j^(th) user, respectively. Multiplying I_(or) by (1+i)gives [I_(or)+I_(or)(i)] where I_(or)(i)=I_(oc) thereby allowing bothintra-cell and inter-cell interference to be accounted for in η_(UL). Ascan be seen from Equation 1, when η_(UL) tends to one, noise rise tendsto infinity.

Once η_(UL) is calculated, noise rise is obtained according to:

$\begin{matrix}{{Noise\_ rise}_{d\; B} = {{- 10} \cdot {{\log\left\lbrack {1 - {\left( {1 - \overset{\_}{\alpha_{UL}} + i + \overset{\_}{i\;\beta_{UL}}} \right){\sum\limits_{j = 1}^{N}\frac{1}{1 + \frac{W}{\rho_{j}R_{j}v_{j}}}}}} \right\rbrack}.}}} & {{Equation}\mspace{14mu}(3)}\end{matrix}$

In FIG. 1, steps for monitoring congestion in the UL based on UEmeasurements in a CDMA system having MUD capabilities are shown andindicated generally with reference number 10.

The method begins with step 12 by calculating the UL load factor(η_(UL)) preferably using equation 2, as explained above. In step 14,Equation 3 is preferably used to calculate the noise rise, as alsoexplained above. The value of noise rise is proportional to congestionand is therefore evaluated in step 16 to determine whether congestionrelieving measures should be implemented. If the value of noise rise isabove a predetermined value, congestion relieving measures areimplemented (step 18). The predetermined value of noise rise that isselected for triggering the congestion relieving measures may be anyvalue. By way of example, in one embodiment, the predetermined value isbetween about 6_(dB) and about 10_(dB).

If, in contrast, the value of noise rise is below the predeterminedvalue, the method may start over at step 12. The method may start overat step 12 at a predetermined time interval. The predetermined timeinterval may be any amount of time, as desired. By way of example, inone embodiment, the time interval is between about 3 seconds to about 5seconds.

In another embodiment of the invention, UL congestion detection may bebased on RAN measurements. In this embodiment, both I_(oc) and I_(or)and both α _(UL) and β _(UL) may be defined by reading measurementsavailable at the base station (BS). Therefore, in contrast to the firstembodiment, η_(UL) and noise rise may be calculated without using apredetermined value to obtain I_(oc).

More specifically, η_(UL) is obtained according to:

$\begin{matrix}{\eta_{UL} = {1 - \frac{noise\_ floor}{{total\_ perceived}{\_ interference}}}} & {{Equation}\mspace{14mu}(4)}\end{matrix}$where the noise floor is again all noise that is not related to thesystem and the total perceived interference comprises all non-cancelledinterference at the receiver. Since the elements needed to calculatetotal perceived power are known, the total perceived power may becalculated according to (1− α _(UL))Ior+(1+ β _(UL))Ioc thereby allowingη_(UL) to be calculated according to:

$\begin{matrix}{\eta_{UL} = {1 - \frac{noise\_ floor}{{\left( {1 + \overset{\_}{\beta_{UL}}} \right){Ioc}} + {\left( {1 - \overset{\_}{\alpha_{UL}}} \right){Ior}}}}} & {{Equation}\mspace{14mu}(5)}\end{matrix}$Once η_(UL) is obtained, the effective noise rise is obtained accordingto:

$\begin{matrix}{{Noise\_ rise}_{d\; B} = {10 \cdot {\log\left\lbrack \frac{{\left( {1 + \overset{\_}{\beta_{UL}}} \right){Ioc}} + {\left( {1 - \overset{\_}{\alpha_{UL}}} \right){Ior}}}{noise\_ floor} \right\rbrack}}} & {{Equation}\mspace{14mu}(6)}\end{matrix}$

In FIG. 2, steps for measuring and avoiding congestion in the UL basedon RAN measurements in a CDMA system having MUD capabilities are shownand indicated generally with reference number 50.

The first step 52, is to measure the noise floor. Then, in step 54, tocalculate η_(UL) preferably according to Equation 5, as explained above,where I_(oc), I_(or), α _(UL) and β _(UL) are defined by readingmeasurements available at the BS. In an alternate embodiment, however,the ratio α _(UL) may be calculated according to:

$\begin{matrix}{{\overset{\_}{\alpha}}_{UL} \cong {\frac{\sum\limits_{i = 1}^{M}\left\lbrack {1 - \frac{{\left( {\overset{\_}{{Rx\_ code}{\_ power}_{i}} \cdot {SF}_{i}} \right)/{\overset{\_}{SIR}}_{i}} - {\overset{\_}{Ioc}}_{i}}{\left( {\overset{\_}{{total\_ perceived}{\_ interference}} - \overset{\_}{{Ioc}_{i}}} \right) - \overset{\_}{{Rx\_ code}{\_ power}_{i}}}} \right\rbrack}{M}.}} & {{Equation}\mspace{14mu}(7)}\end{matrix}$In that embodiment, β _(UL) is considered negligible thereby eliminatingthe need for it to be read from the BS receiver. The additionalparameters shown in Equation 7 are identified and defined frommeasurements taken at the BS receiver. By way of explanation, theadditional parameters included in Equation 7 are Received Code Power forUser i (Rx_Code_Power), Spreading Factor for User i (SF_(i)), and Numberof Active Codes in the Timeslot (M).

Once η_(UL) is obtained, noise rise is calculated according to Equation6 in step 56. As with the embodiment shown in FIG. 1, the value of noiserise is proportional to congestion. Therefore, the value of noise riseis evaluated in step 58 to determine whether congestion relievingmeasures should be implemented. If the value of noise rise is above apredetermined value, congestion relieving measures are implemented (step60). Alternatively, if the value of noise rise is below thepredetermined value, the method may start over at step 52 at apredetermined time interval. As with the embodiment described inconjunction with FIG. 1, the predetermined values of noise rise and timeinterval may be any values, as desired.

The implementation of congestion relieving measures may be accomplishedin a variety of ways. For example, the signal-to-noise ratio (E_(b)/N₀)target of certain users can be reduced thereby forcing those users toreduce their transmission power. A drawback of this approach, however,is that those users will experience errors in the informationtransmitted and the quality of the link is greatly reduced.

A preferred method for relieving congestion is to reduce the datatransmission rate of a particular user or users. Users determine theirtransmission power depending on the data transmission rate, spreadingfactor gain and maximum transmission power and path loss. Therefore,reducing the data transmission rate of a particular user, whichimplicitly reduces power, allows the same signal-to-noise ratio to beachieved with the same spreading gain, but with less power. Furthermore,in WCDMA TDD systems, reducing the data transmission rate implies that acertain user is not transmitting at all in a timeslot thereby providingthe additional benefit of relieving congestion for that timeslot.

The preferred method for relieving congestion limits data transmissionrate at the source; therefore no retransmissions are required. Theselection of the user or users to whom the rates will be reduced is madeby considering the transmitted power, received power and class ofservice. Those factors are considered for each user and may beconsidered individually, collectively or as a particular combinationthereof, as desired. The user or users that contribute the most to theinterference and have the lowest service class priority are preferablychosen as candidates for data rate reduction.

The preferred method for relieving congestion is shown in FIG. 3 andindicated generally with reference numeral 100. To begin, transmissionpower, received power and class of service are determined for each userin steps 102, 104 and 106, respectively. Then, in step 108, each user'scontribution to noise rise is calculated. As explained, noise rise maybe calculated according to Equation 3 or Equation 6, as desired.

In step 110, the user that collectively contributes the most to thenoise rise and has the lowest service priority is selected. To determinethe selected user, a predetermined weighting factor may be used for eachparameter. It is important to note that any value may be used for theweighting factor so that the influence of priority and noisecontribution in selecting a user may be adjusted as desired. Furthermoreit may be desirable to use only one of those parameters or,alternatively, it may be desirable to use additional parameters which,like noise contribution and priority, may be weighted as desired. Thecriteria for selecting a user is completely flexible and may be anycriteria which accurately identifies users having data transmissionrates that may be reduced so as to reduce congestion. Therefore, theselected user may, for example, be determined according to:User_selected=W1(priority)+W2(noise contribution).  Equation (8)

In step 112, the data transmission rate of the selected user is reduced.In step 113, the amount of congestion is evaluated to determine whethercongestion has been relieved. If the corresponding reduction in thenoise rise is sufficient to reduce the value of noise rise below thepredetermined value at which congestion is detected, the method ends andcongestion monitoring, as described in conjunction with FIGS. 1 and 2,may continue (step 114). Alternatively, if the congestion has not beenrelieved so that the value of noise rise is below the predeterminedvalue, congestion still exists and the method 100 returns to step 110 or102, as desired, and continues until the congestion is relieved.

Referring now to FIG. 4, a system 200 is shown for controllingcongestion in the UL based on UE measurements. In system 200, congestionin the UL is monitored and controlled using UE measurements. The system200 comprises at least one UE 202, a BS or node-B 214 and a radionetwork controller 210.

The UE comprises a receiver 203 having MUD capabilities, an I_(or)measuring device 204 and an I_(or) signaling device 206. The I_(or)measuring device 204 utilizes information available at the UE 202 tomeasure the amount of interference generated by the system within thecell in which the UE 202 is currently located. As previously explained,that type of interference is referred to as intra-cell interference(I_(or)).

The BS or node-B 214 includes a receiver 205 having a MUD and an I_(or)signal receiver 208. The I_(or) measured by measuring device 204 istransmitted from the I_(or) signaling device 206 of the UE 202 to theI_(or) signal receiver 208 of the BS or node-B 214. The BS or node-B 214communicates the I_(or) to a radio network controller (RNC) 210comprising a radio resource management (RRM) device 212. The RRM 212, inconjunction with the BS or node-B 214, if needed, processes I_(or) sothat the total interference, as affected by the MUD(s) 203, 205, may beobtained. As explained above, the total interference may be obtainedusing I_(or), α _(UL), β _(UL) and i.

Once the total interference is obtained, η_(UL) and noise rise is alsoobtained. If the noise rise is above a predetermined value, each users'contribution to the noise rise is measured. Preferably, each users'transmission power, received power and class of service are alsomeasured. The data transmission rate of the user currently having thehighest contribution to noise rise and the lowest class of service isreduced as needed until the overall noise rise falls below thepredetermined value. In other words, if reducing the data transmissionrate of what was the highest contributor to noise rise is not sufficientto reduce noise rise to below the predetermined value, the methodcontinues by recalculating each users' noise rise contribution andreducing the data transmission rate of the highest contributor.Alternatively, the method may continue by using the current usercalculations and simply reduce the rate of the next highest contributor.

In FIG. 5, another embodiment of a system for controlling congestion inthe UL is shown and indicated generally with reference numeral 300. Insystem 300, congestion in the UL is monitored and controlled using RANmeasurements. The system 300 comprises at least one UE 301, a BS ornode-B 306 and a RNC 308.

The UE 301 comprises a receiver 303 having MUD capabilities. The BS ornode-B 306 includes a receiver 305 having MUD capabilities, an I_(or)measuring device 302 and an I_(oc) measuring device 304. The BS ornode-B 306 communicates the I_(or) and I_(oc) to a radio networkcontroller (RNC) 308 comprising a radio resource management (RRM) device310. The RRM 310, in conjunction with the BS or node-B 306, if needed,processes I_(or) and I_(oc) so that the total interference, as affectedby the MUD(s) 303, 305, may be obtained. As explained above, the totalinterference may be obtained using I_(or), I_(oc), α _(UL), and β _(UL).

Once the total interference is obtained, η_(UL) and noise rise is alsoobtained. If the noise rise is above a predetermined value, each users'contribution to the noise rise is measured. Preferably, each users'transmission power, received power and class of service is alsomeasured. The data transmission rate of the user currently having thehighest contribution to noise rise and the lowest class of service isreduced as needed until the overall noise rise falls below thepredetermined value, as explained in connection with FIG. 4.

Although the present invention has been described in detail, it is to beunderstood that the invention is not limited thereto, and that variouschanges can be made therein without departing from the spirit and scopeof the invention, which is defined by the attached claims.

What is claimed is:
 1. A wireless code division multiple access (CDMA)user equipment (UE) comprising: a receiver having multi-user detectioncapabilities; an intra-cell interference measuring device configured tomeasure intra-cell interference with respect to a plurality of differentuser signals; and an intra-cell interference signaling device configuredto transmit signals indicative of intra-cell interference with respectto a plurality of different user signals from which congestion controlis based, wherein the receiver is configured to: calculate a noise risevalue based on the measured intra-cell interference; implementcongestion control measures on a condition that the calculated noiserise is above a predetermined threshold; and receive congestion controlsignals responsive to transmitted signals indicative of intra-cellinterference which effect a reduction in a transmission rate at the UEon a condition that the UE is contributing the most to noise rise andhas a lowest class of service.
 2. A radio network controller (RNC),comprising: a radio resource management (RRM) device configured tocalculate a noise rise value based on received intra-cell interferenceand inter-cell interference measurements taken by a user equipment (UE)that are received via a base station, wherein the RNC implementscongestion relieving measures on a condition that the calculated noiserise is greater than a predetermined value, wherein the congestionrelieving measures include: determining a class of service for all UEscommunicating with the base station; calculating a contribution to noiserise for each UE; selecting a UE that is currently contributing the mostto noise rise and has a lowest class of service; and adjusting a datatransmission rate of the selected UE.
 3. The RNC according to claim 2,wherein the RRM device is further configured to account for an effect ofmultiple user detection capabilities of the base station whencalculating the noise rise value.
 4. The RNC according to claim 2,wherein the congestion relieving measures further include adjusting asignal-to-noise ratio target of the selected UE.
 5. A method forcontrolling congestion in wireless communications by a code divisionmultiple access user equipment (UE), the method comprising: calculatinga noise rise; and implementing a congestion relieving measure on acondition that the noise rise is above a predetermined threshold,wherein the congestion relieving measure includes: calculating a noiserise contribution of each UE; selecting a first UE having a highestcontribution to the noise rise; reducing a transmission rate of thefirst UE; and adjusting a target signal-to-interference ratio of thefirst UE.
 6. The method of claim 5, wherein the calculation of the noiserise is based on an intra-cell interference measured at the first UE. 7.The method of claim 6, wherein an inter-cell interference is calculatedusing a predetermined ratio to the intra-cell interference.
 8. Themethod of claim 5, wherein the calculation of the noise rise is based onan intra-cell interference and an inter-cell interference measured at abase station.
 9. The method of claim 5, further comprising:recalculating the noise rise contribution of each UE after reducing thetransmission rate of the first UE; selecting a second UE having thehighest contribution to noise rise; and reducing a transmission rate ofthe second UE.
 10. The method of claim 5, further comprising: selectinganother UE having the next highest contribution to noise rise on acondition that the noise rise is still above the predeterminedthreshold; and reducing a transmission rate of the selected another UE.11. The method of claim 5, wherein the selecting includes considering aclass of service of each UE.